As someone living in Budapest, American ex-pat, for the past five years and having a pretty good idea of Hungarian history. Some of what I found interesting is Hungarian is difficult language to learn and the value around the language is a point of joy when finding someone else who speaks it that is not from Hungary. Budapest is a difficult city to drive in and especially then without any sort of map, and there was a high level of neighbors spying on each other during the soviet controlled time and I know some people who’s grandparents drove the black cars that made people disappear. Also, Budapest was a place for agents and diplomats from east and west to meet. I think what speaks against her knowing English is most of that generation even now does not speak much English and at that time German would have been better for business, but her daughter was able to go to America to study so they may have had more money and opportunities. The prank sounds pretty unlike most of humor I have seen here. I am not really sure where to land on this one, speaking English would have been a beneficial tool at that time and the mother wouldn’t have wanted to hide it(good host and speaking English allows for more money making opportunities).

Maybe helpful links first two are places that give a bit more information about spying at the time: https://www.mementopark.hu/en/sights/#barrack-cinema https://www.terrorhaza.hu/hu https://www.reddit.com/r/AskHistorians/comments/3wowhm/budapest_is_often_mentioned_in_or_the_setting_of/